C# in Depth

198 CHAPTER 7 Concluding C# 2: the final featuresis never read from or written to. It’s almost always going to be useless… unless we happento know that it will be used by reflection. Listing 7.9 is a complete class demonstratingthis.Listing 7.9Class containing an unused fieldpublic class FieldUsedOnlyByReflection{int x;}If you try to compile listing 7.9, you’ll get a warning message like this:FieldUsedOnlyByReflection.cs(3,9): warning CS0169:The private field 'FieldUsedOnlyByReflection.x' is never usedThat’s the output from the command-line compiler. In the Error List window of VisualStudio, you can see the same information (plus the project it’s in) except that you don’tget the warning number (CS0169). To find out the number, you need to either selectthe warning and bring up the help related to it, or look in the Output window, wherethe full text is shown. We need the number in order to make the code compile withoutwarnings, as shown in listing 7.10.Listing 7.10Disabling (and restoring) warning CS0169public class FieldUsedOnlyByReflection{#pragma warning disable 0169int x;#pragma warning restore 0169}Listing 7.10 is self-explanatory—the first pragma disables the particular warning we’reinterested in, and the second one restores it. It’s good practice to disable warnings foras short a space as you can, so that you don’t miss any warnings you genuinely ought tofix. If you want to disable or restore multiple warnings in a single line, just use acomma-separated list of warning numbers. If you don’t specify any warning numbersat all, the result is to disable or restore all warnings in one fell swoop—but that’s a badidea in almost every imaginable scenario.7.5.2 Checksum pragmasYou’re very unlikely to need the second form of pragma recognized by the Microsoftcompiler. It supports the debugger by allowing it to check that it’s found the rightsource file. Normally when a C# file is compiled, the compiler generates a checksumfrom the file and includes it in the debugging information. When the debugger needsto locate a source file and finds multiple potential matches, it can generate the checksumitself for each of the candidate files and see which is correct.Now, when an ASP.NET page is converted into C#, the generated file is what the C#compiler sees. The generator calculates the checksum of the .aspx page, and uses aLicensed to Rhona Hadida